Myasthenia gravis is a chronic condition that causes muscles to tire and weaken easily. For example, if you have myasthenia gravis, you may notice that during a meal, your jaw muscles become tired and weak, interfering with your ability to chew food. After you have rested for a little while, the muscles may become strong again, allowing you to resume eating.
This waxing-and-waning weakness of muscles, worsening with use and improving with rest, is a hallmark of this particular disease. There typically are periods when you may notice more symptoms (called an exacerbation), interspersed with periods when symptoms decrease or disappear (remission).
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The disease most commonly affects muscles that control eye and eyelid movement, so the first symptoms you notice may be eyelid drooping and/or blurred or doubled vision. The majority will go on to develop weakness in other muscle groups within one or two years.
Myasthenia gravis affecting multiple muscle groups throughout the body is called generalized myasthenia gravis. Other common muscle groups that are affected may make it difficult for you to chew, swallow, smile, shrug, lift your arm up, grip, rise to a stand, or walk up stairs. When the muscles necessary for breathing are affected, a patient is said to be in myasthenic crisis. This is a life-threatening situation.
Though anyone can develop myasthenia gravis, those most likely to do so are women between age 20 and 40 or men between age 50 and 70. If a woman with myasthenia gravis gives birth, the baby may have some temporary, and potentially life-threatening, muscle weakness (neonatal myasthenia) because of antibodies that have transferred from the mother's bloodstream. Typically, during the baby's first weeks of life, the antibodies are cleared from the baby's circulation and the baby develops normal muscle tone and strength.
What Causes Myasthenia Gravis?
Under normal conditions, nerves direct your muscles to work by sending a message through an area called a receptor. The chemical that delivers the message is called acetylcholine. When acetylcholine binds to a nerve receptor, your muscle knows to contract. In myasthenia gravis, you have fewer acetylcholine receptors than you need.